TOPIC: subnet calculation

i'm a little bit confuse about subnet calculation..
as i know, class A begin with 1.x.x.x - 126.x.x.x,class B begin with 128.0.x.x - 192.255.x.x and class C begin with 192.0.0.x - 223.255.255.x
at my office, they use 10.20.x.x ip with 255.255.252.0 netmask..
10.20.x.x is class A range but 255.255.252.0 is class B netmask..
is it valid?or is it my missunderstand about ip calculation..

Hello apit, i think you are a bit confused about subnetting. My advise is that you study about ip subnetting and in the beginning you can use a subnet calculator to help you out. Solarwinds offers a subnet calculator for free and it is a good one, visit www.solarwinds.net.
Now for the given subnet, yes it is valid, it is a Class A address subnetted with 1022 hosts per subnet (correct me if I'm wrong but i'm steel sleepy :? ). Hope i helped......
Cheerz,